Solar panels electrical connection to mains.

Seems to happen less often now ...

Are there any regs that need to be followed if the solar energy isn't going to the grid - just used stored/used locally for things like hot water?

but what if the home energy storage system was to autodisconnect itself from the grid should grid voltage drop to zero?

As via a smart changeover switch if you had a generator.

This then means the house would be "islanded" and then running off its own batteries computer UPS style....

Obviously the battery will eventually discharge if the grid supply does not return.

It *has* to do that. Some hybrid inverters have a separate output which only connects to local loads, not to the grid, obviously great care needs to be taken not to somehow connect that output to the grid ...

As long as it's a compliant inverter, any competent sparkie can wire it up, you might choose in the inverter settings to set it to export a maximum of 0 amps, or you might let it charge a battery, or you might let the grid have it for free. Only needs the sparkie to be MCS registered if you want paying for your exports.

In fact it has to disconnect if there's a certain amount of voltage drop, or frequency drop (and probably for voltage/frequency increases too?)

I dislike these closed shops!

Can a MCS registered sparkie signed the installation off? Say by making the last (re)connection and checking equipment etc conforms to the relevant standards / certs?

If there's no physical connection - eg a separate immersion coil in your hot water, then I think only the usual BS7671 electrical regs apply.

If you're consuming it for local loads, then if you are able to back-drive the grid (ie inverter connected to circuit which is connected to grid via CU) then it needs G98, even if you never plan to export - because it could still enliven the grid.

If you have a transfer switch such that your loads switch over from grid power and become isolated when powered by the inverter (like when running a generator), then I think you don't need G98, but not sure if the transfer switch needs some kind of approval.

Generally though it's hard to run loads fully isolated, because you need to supply enough to cope with current pulses like inrush and motor starting currents. You have to think a lot harder about what your loads actually need. When grid connected, there's always the grid there to provide the extra.

Theo

When we are told about electricity generation capacity we are often told the number of houses that can be supplied rather than a figure in MW. When this is done it is assumed that each house consumers 500W.

That is of course the arithmetic average over 24 hours, seven days etc where I was talking about the diversity figures the DNO will use to calculate the likely peak loads on the secondary side of the substation.

That may be more typical than my house ... no hairdryers or hair straighteners here

And that windmills provide energy 100% of the time Reminds me of the apocry[hal story of an Apple competition in which Apple offereed a free Apple II to someone who came up with the best used for one. My entris of 'as a rather fragile doorstop, or to hull at vagrants in the street' did not win. No, someone said 'with *additional hardware and sofwtare* and Apple II could put a man on the moon! With 'additional hardware and software', like millions of nuclear power stations, renewable energy could run the world.

What's to stop the meter from going backwards if you feed electricity back into the grid (assuming it's the spinning disc type)?

Isn't part of the  list of requirements to have a compliant installation, that you have a 'smart' meter, and so nothing 'dumb' enough to start going backwards ?

That's what I'd be thinking, with all the pathetic feed-in tariffs . . . would need a decent battery mind

That could come later, if/when feed-in makes sense.

Yes, good points. Hot water, and hot water using machines, are high current (but maybe they don't pulse too violently?), so that'd need thinking about. It's hardly worth doing for a TV and a couple of LED lights! And I think space heating has to get its power elsewhere.

I suppose with a battery you could do everything with DC: charge from solar, charge from grid, run loads from battery inverter - much like a boat where you'd get either engine or shore power. No danger of backfeeding the grid because the inverted AC only powers loads.

But you're limited by the AC->DC->AC conversion, so if you only have a 3kW inverter then you can't power inrush currents that need 4kW for 1 second.

Beware that feed in (SEG) payments need an MCS certified install. You can't retrofit that afterwards. Although there might be a way to get a partial MCS install - eg 'Dear Mr Installer, please install some more panels and a new inverter to my old system' which might be enough to get you the MCS tickbox.

Hot water loads are fairly constant, but machines have motors with starting currents. I imagine say an induction cooker might too.

(being able to cover your cooking load from battery is quite handy, as it can allow agile tariffs to make sense, or getting paid for peak load shaving)

Theo

In message snipped-for-privacy@mid.individual.net>, at 10:19:34 on Sat, 1 Apr

As someone else commented, this doesn't work so well in a power cut.

We had one for an hour last week because "another utility" (unspecified, but on balance of probability the water company fixing a leak) had dug a trench in the road and hit a power cable (probably 15kV between local substation and upstream substation, but it could have been the very local 240v three-phase from substation to properties) and the power company switched it off so it was safe for the workers to investigate.

For such a short outage (an actual break would typically take at least half a day to fix, and if longer they start bringing in portable generators for registered vulnerable users) they must have concluded no permanent damage done to the power cable, and switched it all back on again.

Of course, when the power is off like that, you also don't want houses feeding into the 'floating' local distribution system, which you thought was safe to work on.

In message <u09at8$1tvv5$ snipped-for-privacy@dont-email.me, at 14:17:24 on Sat, 1 Apr

That sounds right. I've also seen studies by National Grid as part of navel-gazing about electric car chargers, which says local 240v distribution (which in many rural areas is still wires on poles) is typically sized at an instantaneous average 1.2kW (ie 5amp) per property on any one shared physical three-phase cabling.

And then people start randomly installing and switching on 7kW car chargers, which tend to be on for longer period than the 7kW electric showers the infrastructure was installed to cope with.

In message snipped-for-privacy@mid.individual.net>, at 14:31:14 on Sat, 1 Apr

That's peak consumption, what's more important here is *average* consumption (with the peaks smoothed out by local diversity of demand - eg not every house in the street switching on an electric kettle during the advert break in Coronation Street).